hrid-dese ’rjuna tisthati
In this verse the word yantra, or “machine,” means that in any species of life, we are traveling in bodies that are like machines provided by material nature. Sometimes we are moving to higher species, sometimes to lower species. But if, by the mercy of the spiritual master and Krsna, one gets the seed of devotional service and cultivates it, he can become free from the cycle of birth and death. Then his life is successful. Otherwise, he has to travel up and down the different species of life, becoming sometimes a blade of grass, sometimes a lion, and so forth.